Frequency and match tuning in one state and frequency tuning in the other state

ABSTRACT

Systems and methods for frequency and match tuning in one state S 1  and frequency tuning in another state S 2  are described. The systems and methods include determining one or more variables for the states S 1  and S 2 , and tuning a frequency for the state S 1  of a radio frequency (RF) generator based on the one or more variables.

CLAIM OF PRIORITY

The present patent application claims the benefit of and priority, under35 U.S.C. § 119(e), to U.S. provisional patent application No.62/402,608, filed on Sep. 30, 2016, and titled “Frequency and MatchTuning in One State and Frequency Tuning in the Other State”, which isincorporated by reference herein in its entirety.

FIELD

The present embodiments relate to frequency and match tuning in onestate and frequency tuning in the other state.

BACKGROUND

In some plasma processing systems, a radio frequency (RF) signal isprovided to an electrode within a plasma chamber. The RF signal is usedgenerate plasma within the plasma chamber. The plasma is used for avariety of operations, e.g., clean substrate placed on a lowerelectrode, etch a substrate, etc. During processing of the substrateusing the plasma, the RF signal transitions between two states.

It is in this context that embodiments described in the presentdisclosure arise.

SUMMARY

Embodiments of the disclosure provide systems, apparatus, methods andcomputer programs for frequency and match tuning in one state andfrequency tuning in the other state. It should be appreciated that thepresent embodiments can be implemented in numerous ways, e.g., aprocess, an apparatus, a system, a device, or a method on a computerreadable medium. Several embodiments are described below.

In multi-state pulsing where an impedance matching circuit and afrequency of a radio frequency (RF) generator are both being used totune plasma impedance, feedback is used from each state individually,but the tuning is greatly improved if each state of a plurality ofpulsing states is aware of what the other state is doing. One of thestates is a lower powered state and another one of the states is ahigher powered state. The lower powered state has a lower amount ofpower, e.g., root mean square power, etc., compared to the higherpowered state. A feedback mechanism which exists between the two or morepulsing states and the impedance matching circuit is described to avoidinstabilities and to achieve minimum reflected power. For example, for a13.56 megahertz (MHz) centered RF generator which is used to drive abias, as power supplied by the RF generator is increased, a load becomesincreasingly more capacitive, and as the power supplied by the RFgenerator is decreased, the load becomes increasingly more inductive. Asa result for a two state bias pulsing scheme, with a given fixed matchposition, e.g., impedance, capacitance, inductance, positions of circuitcomponents, etc., of the impedance matching circuit, the lower poweredstate tunes to a lower frequency than the high powered state. In manycases, the high powered state will be tuned with the impedance matchingcircuit as that will be the state which does the etching and it isdesirable to have a low reflected power in the etch state. However,setting a first state frequency, e.g., the high powered state frequency,is important for success of frequency tuning for a second state, e.g.,the low powered state. If the frequency for the first state is set toolow, then there is not enough frequency range on the RF generator forpower of the second state to reach a set point, and if the high poweredstate frequency is set too high, it can infringe on a change in powerwith respect to change in plasma impedance, e.g., dP/dZ, etc., or createplasma instability depending on chemistry. The systems and methodsdescribed herein provide an auto sweep of the frequency in the firststate, e.g., S1, but using feedback from the second state to determinewhich direction to go and when to stop. In one embodiment, the state S1is the high powered state.

This is different from some frequency tuning algorithms that rely onfeedback from its own state, not other states. For example, in a methodof frequency tuning, during each state, the impedance matching circuitis in the fixed match position while the RF generator adjusts its RFfrequency to achieve a lowest reflection coefficient. As anotherexample, in pulsing schemes with the two states and thus two impedances,the impedance matching circuit is fixed such that during each state, areal part of impedance is being tuned by the impedance matching circuitand a reactive part of the impedance is tuned by the frequency. Thismeans that there is some finite reflected power in both the states.

In some embodiments, the methods, described herein, include impedancetuning in dual state pulsing. For example, the impedance matchingcircuit is used to tune in one state, e.g., the high powered state orthe low powered state, to achieve nearly 0 reflected power, andfrequency of the RF generator is used to tune the other state, e.g., thelow powered state or the high powered state. A match tuned state inwhich the impedance matching circuit is used to tune will achieve zeroor nearly zero reflected power but a frequency tuned state in which thefrequency of the RF generator is used to tune may have slightly higherreflected power. Depending on what the frequency is in the match tunedstate, an iterative process to find an optimal fixed frequency of the RFgenerator for the match tuned state is applied. The iterative processoravoids running in an issue of not having enough frequency range in thefrequency tuned state, or instabilities in one or both of the states.

In one embodiment, a method for achieving reduction in power reflectedtowards an RF generator is described. The method includes providing aplurality of set points to the RF generator. The set points include afrequency set point for a first state of a digital pulsed signal, afrequency set point for a second state of the digital pulsed signal, apower set point for the first state of the digital pulsed signal, and apower set point for the second state of the digital pulsed signal. Themethod further includes adjusting an impedance matching circuit toreduce a variable for the first state to be below a pre-determinedvariable threshold. The variable is associated with the RF generator.The method includes determining whether the variable for the first stateis stable and adjusting the frequency set point for the second stateupon determining that the variable for the first state is stable. Theoperation of adjusting the frequency set point for the second state isperformed to reduce the variable for the second state to be lower than apre-set variable threshold. The method also includes determining whetherthe variable for the second state is stable. The method includeschanging the frequency set point for the first state in response todetermining that the variable for the second state is not stable toachieve the reduction in power reflected towards the RF generator.

Some advantages of the herein described systems and methods includeautomatically finding optimal frequencies for application in bothstates. For example, one or more variables, e.g., gamma, or voltagestanding wave ratio, etc., are calculated during the state S1 and astate S2, e.g., the low powered state, the second state, etc. The one ormore variables are used to tune a frequency of the RF generator duringthe state S1 while achieving a low gamma during the state S1, a lowgamma during the state S2, a stable gamma during the state S1, and astable gamma during the state S2. By tuning the frequency of the RFgenerator during the state S1, there is a reduction in power that isreflected towards the RF generator from a plasma chamber. The reductionin the reflected power increases efficiency in processing of a wafer inthe plasma chamber and also reduces chances of damage to componentswithin the RF generator.

Other aspects will become apparent from the following detaileddescription, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments may best be understood by reference to the followingdescription taken in conjunction with the accompanying drawings.

FIG. 1 is a block diagram of an embodiment of a plasma tool forfrequency and match tuning in one state and frequency tuning in theother state.

FIG. 2 is a flowchart of an embodiment of a method for tuning afrequency set point for a state S1 based on one or more variables forthe state S1 and the one or more variables for a state S2.

FIG. 3 is a diagram of an embodiment of a graph to illustrate the twostates S1 and S2 of a radio frequency (RF) signal that is generated byan RF generator and a graph to illustrate the two states S1 and S2 of apulsed signal.

FIG. 4 is a diagram of embodiments of multiple Smith charts toillustrate that with an increase in power difference between power setpoints for the states S1 and S2, there is a decrease in a tunablefrequency range for the state S2.

FIG. 5 is a diagram of embodiments of multiple Smith charts toillustrate that a change in a frequency set point for the state S1 helpsachieve a desirable plasma impedance at an output of the RF generator.

FIG. 6A is a diagram of an embodiment of a method for tuning thefrequency set point for the state S1 based on the one or more variablesfor the state S1 and the one or more variables for the state S2.

FIG. 6B is a diagram of an embodiment of a method for tuning thefrequency set point for the state S1 based on the one or more variablesfor the state S1 and the one or more variables for the state S2.

DETAILED DESCRIPTION

The following embodiments describe systems and methods for frequency andmatch tuning in one state and frequency tuning in the other state. Itwill be apparent that the present embodiments may be practiced withoutsome or all of these specific details. In other instances, well knownprocess operations have not been described in detail in order not tounnecessarily obscure the present embodiments.

In some embodiments, the methods, described herein, use feedback from aradio frequency (RF) generator from both states S1 and S2 to scan afrequency for a match tuned high powered state, which is the state S1,while utilizing a frequency tuning algorithm for the fixed matchfrequency tuned low powered state, which is the state S2. The fixedmatch frequency tuned low powered state is one in which an impedancematching circuit (IMC) is not tuned, e.g., has a fixed impedance, hasfixed positions of circuit components, has fixed capacitance, has fixedinductance, etc.

In various embodiments, one of the methods is executed as follows. Forall processes, e.g., recipes, etc., the state S1 bias frequency is setto 13.56 megahertz (MHz) or middle of a frequency tuning range, whilethe state S2 bias frequency is set to 12.882 MHz or a bottom of thefrequency tuning range. It should be noted that instead of 13.56 MHz,another pre-determined frequency value, e.g., 13 MHz, 13.2 MHz, or 13.5,is used and instead of 12.882 MHz, another pre-determined frequencyvalue, e.g., 12 MHz, 12.2 MHz, or 12.5 MHz, is used. When the RFgenerator is turned on to generate an RF signal, the IMC will start totune an impedance for the state S1, and the state S2 frequency will stayat 12.882 MHz or another pre-determined value until a reflectioncoefficient, such as gamma, in the state S1 drops below a certainthreshold, e.g., 0.2 gamma, etc., signaling that the state S1 is nearlytuned and the IMC will not be tuned much. At this point the state S2frequency will start to scan at a pre-set frequency step size and apre-set step time, and once the gamma of the state S2 drops below aspecific value, e.g., 0.7 gamma, 0.6 gamma, 0.5 gamma, 0.2 gamma, etc.,then the state S2 frequency tuning algorithm initiates and tune to alowest reflection coefficient, such as gamma, for the state S2. Thedelay before the state S2 frequency tuning algorithm in waiting for theimpedance matching circuit to tune is useful, otherwise the state S2frequency tuning algorithm may find false minimas in the reflectioncoefficient. Then if state S1 and S2 power set points are met and thereflection coefficients in both the states S1 and S2 are stable then amatching condition is achieved. However, if either the state S1 or stateS2 power set point is not met or if the reflection coefficient in eitherstate is not stable based on standard deviation values calculated by theRF generator, then both states frequency will freeze, and the state S1frequency will start to scan upwards towards a higher frequency ordownwards towards a lower frequency with a predetermined step size and apredetermined step time, and then waits for the impedance matchingcircuit to tune by detecting the gamma threshold for the state S1 andstability. If there is no stabilization, the frequency scan continuesuntil the state S1 gamma is low and stable. Then the state S2 frequencytuning will start again. If the state S2 gamma is low and stable, themethod stops. If the state S2 gamma is high or unstable, the methodstarts again with the state S1 until a solution is found or none isfound and the process is found to be outside of a process window, e.g.,a process recipe, outside of chemistry parameters, outside of gapparameters, outside of etch parameters, outside of depositionparameters, etc.

FIG. 1 is a block diagram of an embodiment of a plasma tool 100 forfrequency and match tuning in one state and frequency tuning in theother state. The plasma tool 100 includes a radio frequency (RF) powergenerator 102, a host computer 104, an IMC 106, a plasma chamber 108, adriver system 150, and a motor system 152. The RF generator 102 is a 400kilohertz (kHz), or a 2 MHz, or a 13.56 MHz, or a 27 MHz, or a 60 MHz RFgenerator. Examples of the host computer 104 include a desktop computer,or a laptop computer, or a smartphone, or a tablet, etc.

The RF generator 102 includes a digital signal processor (DSP) 110, apower controller PWRS1, another power controller PWRS2, an autofrequency tuner (AFT) AFTS1, another auto frequency tuner AFTS2, an RFpower supply 112, a sensor system 114, and a driver system 120. Examplesof the RF power supply 112 include an RF oscillator. As used herein, aprocessor is an application specific integrated circuit (ASIC), or aprogrammable logic device (PLD), or a central processing unit (CPU), ora microprocessor, or a microcontroller. As used herein, a controller isapplication specific integrated circuit (ASIC), or a programmable logicdevice (PLD), or a central processing unit (CPU), or a microprocessor,or a microcontroller, or a processor. Examples of the sensor system 114include one or more sensors, e.g., a complex voltage and current sensor,a voltage reflection coefficient sensor, an impedance sensor, adelivered power sensor, a voltage sensor, a supplied power sensor, areflected power sensor, etc. In some embodiments, the terms suppliedpower and forward power are used interchangeably herein. The deliveredpower is a difference between the supplied power and the reflectedpower. Examples of the driver system 120 include one or moretransistors.

The plasma chamber 108 includes a chuck 126 and an upper electrode 128that faces the chuck 126. The upper electrode 128 is coupled to a groundpotential. The plasma chamber 108 also includes other components (notshown), e.g., an upper dielectric ring surrounding the upper electrode128, an upper electrode extension surrounding the upper dielectric ring,a lower dielectric ring surrounding the chuck 126, a lower electrodeextension surrounding the lower dielectric ring, an upper plasmaexclusion zone (PEZ) ring, a lower PEZ ring, etc. The upper electrode122 is located opposite to and facing the chuck 126, which includes alower electrode. For example, the chuck 126 includes a ceramic layerthat is attached to top of the lower electrode and a facility plate thatis attached to bottom of the lower electrode. The upper electrode 122 iscoupled to a ground potential.

A substrate 130, e.g., a semiconductor wafer, is supported on an uppersurface of the chuck 126. Integrated circuits, e.g., an applicationspecific integrated circuit (ASIC), a programmable logic device (PLD),etc., are developed on the substrate 130 and the integrated circuits areused in a variety of devices, e.g., cell phones, tablets, smart phones,computers, laptops, networking equipment, etc. The lower electrode ismade of a metal, e.g., anodized aluminum, alloy of aluminum, etc. Also,the upper electrode 128 is made of a metal, e.g., aluminum, alloy ofaluminum, etc.

The upper electrode 128 includes one or more holes that are coupled to acentral gas feed (not shown). The central gas feed receives one or moreprocess gases from a gas supply (not shown). Examples of the one or moreprocess gases include an oxygen-containing gas, such as O₂. Otherexamples of the one or more process gases include a fluorine-containinggas, e.g., tetrafluoromethane (CF₄), sulfur hexafluoride (SF₆),hexafluoroethane (C₂F₆), etc.

Examples of the motor system 152 include one or more electric motors,e.g., a stepper motor, etc. The driver system 150 includes one or moredrivers, e.g., one or more transistors, etc. A driver, e.g., a circuitof one or more transistors, a current generator, etc., of the driversystem is coupled to a corresponding motor of the motor system 152. Forexample, a first driver of the driver system 150 is coupled to a firstmotor of the motor system 152 and a second driver of the driver system150 is coupled to a second motor of the motor system 152. The processor132 is coupled to the driver system 150 via a cable 154. A circuitcomponent, e.g., an inductor, a capacitor, etc., of the IMC 106 iscoupled to a corresponding motor of the motor system 152 via aconnection mechanism, e.g., one or more shafts, or a combination of oneor more gears and shafts. For example, a first circuit component of theIMC 106 is coupled to a first motor of the motor system 152 and a secondcircuit component of the IMC 106 is coupled to a second motor of themotor system 152.

The sensor system 114 is coupled to an output 116 of the RF generator102, and the output 116 is also an output of the RF power supply 112. Insome embodiments, the sensor system 114 is located outside a housing ofthe RF generator 102 and is coupled to the output 116 of the RFgenerator 102. For example, the sensor system 114 includes a directionalcoupler coupled to an oscilloscope for measuring the voltage reflectioncoefficient at the output 116. In various embodiments, the sensor system114 is coupled to any point on the RF cable 122. In several embodiments,the sensor system 114 is coupled to an input of the IMC 106 or to anoutput of the IMC 106. In some embodiments, the sensor system 114 iscoupled to a point on an RF transmission line 124. The RF transmissionline 124 includes a metal rod that is surrounded by an insulator that isfurther surrounded by a sheath. The metal rod is coupled to a cylindervia an RF strap and the cylinder is coupled to the chuck 126.

The DSP 110 is coupled to the power controllers PWRS1 and PWRS2, and tothe auto-frequency tuners AFTS1 and AFTS2. Moreover, the powercontrollers PWRS1 and PWRS2 and the auto-frequency tuners AFTS1 andAFTS2 are coupled to the driver system 120. The driver system 120 iscoupled to the RF power supply 112. The RF power supply 112 is coupledvia the output 116 and an RF cable 122 to the input of the IMC 106. Theoutput of the IMC 106 is coupled via the RF transmission line 124 to thelower electrode of the chuck 126. In some embodiments, the RFtransmission line 124 is coupled to the upper electrode 128 and thelower electrode 126 is coupled to the ground potential.

The IMC 106 includes electric circuit components, e.g., inductors,capacitors, etc. to match an impedance of a load coupled to the outputof the IMC 106 with an impedance of a source coupled to the input of theIMC 106. For example, the IMC 106 matches an impedance of the plasmachamber 108 and the RF transmission line 124 coupled to the output ofthe IMC 106 with an impedance of the RF generator 102 and the RF cable112, which is coupled to the input of the IMC 106. In one embodiment,one or more of the electrical circuit components of the IMC 106 aretuned to facilitate a match between an impedance of the load coupled tothe output of the IMC 106 with that of the source coupled to the inputof the IMC 106. The IMC 106 reduces a probability of power beingreflected a direction towards the source, e.g., from the load towardsthe source.

The host computer 104 includes a processor 132 and a memory device 134.The processor 132 is coupled to the memory device 134. Examples of amemory device include a random access memory (RAM) and a read-onlymemory (ROM). To illustrate, a memory device is a flash memory, a harddisk, or a storage device, etc. A memory device is an example of acomputer-readable medium. The processor 132 is coupled to the sensorsystem 114 via a cable 136 and to the DSP 110 via a cable 138. Examplesof the cable 136 or the cable 138 include a cable that is used totransfer data in a serial manner, a cable that is used to transfer datain a parallel manner, and a cable that is used to transfer data byapplying a universal serial bus (USB) protocol.

A control circuit of the processor 132 is used to generate a pulsedsignal 140, e.g., a transistor-transistor logic (TTL) signal, a digitalpulsing signal, a clock signal, a signal with a duty cycle, etc.Examples of the control circuit of the processor 132 includes a TTLcircuit.

The pulsed signal 140 includes the states S1 and S2. For example, thestate S1 of the pulsed signal 140 has a logic level of one and the stateS2 of the pulsed signal 140 has a logic level of zero. In variousembodiments, the states S1 and S2 execute once during a clock cycle ofthe pulsed signal 140 and repeat with multiple clock cycles. Forexample, the clock cycle includes the states S1 and S2 and another clockcycle includes the states S1 and S2. To illustrate, during a half periodof a clock cycle, the state S1 is executed and during the remaining halfperiod of the clock cycle, the state S2 is executed.

In some embodiments, each of the states S1 and S2 has a duty cycle of50%. In several embodiments, each of the states S1 and S2 has adifferent duty cycle. For example, the state S1 has an x % duty cycleand the state S2 has a duty cycle of (100−x) %, where x is an integer.

In various embodiments, instead of the control circuit of the processor132, a clock source, e.g., a crystal oscillator, etc., is used togenerate an analog clock signal, which is converted by ananalog-to-digital converter into a digital signal similar to the pulsedsignal 140. For example, the crystal oscillator is made to oscillate inan electric field by applying a voltage to an electrode near the crystaloscillator. In some embodiments, instead of the processor 132, a digitalclock source generates the pulsed signal 140. In various embodiments,the pulsed signal 140 is generated by the control circuit located withina master RF generator (not shown) and sent to the RF generator 102 via acable. In several embodiments, the pulsed signal 140 is generated by thecontrol circuit within the RF generator 102, which acts as a mastergenerator for other RF generators to use.

The processor 132 accesses a recipe from the memory device 134. Examplesof the recipe include a power set point for the state S1, a power setpoint for the state S2, or a frequency set point for the state S1, or afrequency set point for the state S2, or a chemistry of the one or moreprocess gases, or a gap between the upper electrode 128 and the chuck126, or a combination thereof. The processor 132 sends an instructionwith the pulsed signal 140, the power set point for the state S1, thepower set point for the state S2, the frequency set point for the stateS1, and the frequency set point for the state S2 to the DSP 110 via thecable 138.

The DSP 110 determines from the instruction that the power set point forthe state S1 is to be applied during the state S1 of the pulsed signal140, the power set point for the state S2 is to be applied during thestate S2 of the pulsed signal 140, the frequency set point for the stateS1 is to be applied during the state S1 of the pulsed signal 140, andthe frequency set point for the state S2 is to be applied during thestate S2 of the pulsed signal 140. During the state S1 of the clockcycle, the DSP 110 sends the power set point for the state S1 to thepower controller PWRS1. Similarly, during the state S2 of the clockcycle, the DSP 110 sends the power set point for the state S2 to thepower controller PWRS2. Moreover, during the state S1 of the clockcycle, the DSP 110 sends the frequency set point for the state S1 to theauto-frequency tuner AFTS1. Also, during the state S2 of the clockcycle, the DSP 110 sends the frequency set point for the state S2 to theauto-frequency tuner AFTS2.

Upon receiving the power set point for the state S1, the powercontroller PWRS1 determines an amount of current corresponding to, e.g.,having a one-to-one relationship with, mapped to, linked to, etc., thepower set point for the state S1. Based on the amount of current that isto be generated by the driver system 120 during the state S1, the powercontroller PWRS1 generates a command signal and sends the command signalto the driver system 120. During the state S1, in response to receivingthe command signal, the driver system 120 generates and sends a currentsignal having the amount of current to the RF power supply 112. The RFpower supply 112, upon receiving the current signal generates an RFsignal having the power set point for the state S1 and supplies the RFsignal via the output 116 and the RF cable 122 to the input of the IMC106.

Similarly, upon receiving the power set point for the state S2, thepower controller PWRS2 determines an amount of current corresponding to,e.g., having a one-to-one relationship with, mapped to, linked to, etc.,the power set point for the state S2. Based on the amount of currentthat is to be generated by the driver system 120 during the state S2,the power controller PWRS2 generates a command signal and sends thecommand signal to the driver system 120. During the state S2, inresponse to receiving the command signal, the driver system 120generates and sends a current signal having the amount of current to theRF power supply 112. The RF power supply 112, upon receiving the currentsignal generates the RF signal having the power set point for the stateS2 and supplies the RF signal via the output 116 and the RF cable 122 tothe input of the IMC 106.

Moreover, upon receiving the frequency set point for the state S1, theauto-frequency tuner AFTS1 determines an amount of current correspondingto, e.g., having a one-to-one relationship with, mapped to, linked to,etc., the frequency set point for the state S1. Based on the amount ofcurrent that is to be generated by the driver system 120 during thestate S1, the auto-frequency tuner AFTS1 generates a command signal andsends the command signal to the driver system 120. During the state S1,in response to receiving the command signal, the driver system 120generates and sends a current signal having the amount of current to theRF power supply 112. The RF power supply 112, upon receiving the currentsignal generates the RF signal having the frequency set point for thestate S1 and supplies the RF signal via the output 116 and the RF cable122 to the input of the IMC 106. The RF signal having the power setpoint for the state S1 and the frequency set point for the state S1 isthe RF signal generated during the state S1.

Similarly, upon receiving the frequency set point for the state S2, theauto-frequency tuner AFTS2 determines an amount of current correspondingto the frequency set point for the state S2. Based on the amount ofcurrent that is to be generated by the driver system 120 during thestate S2, the auto-frequency tuner AFTS2 generates a command signal andsends the command signal to the driver system 120. During the state S2,in response to receiving the command signal, the driver system 120generates and sends a current signal having the amount of current to theRF power supply 112. The RF power supply 112, upon receiving the currentsignal generates the RF signal having the frequency set point for thestate S2 and supplies the RF signal via the output 116 and the RF cable122 to the input of the IMC 106. The RF signal having the power setpoint for the state S2 and the frequency set point for the state S2 isthe RF signal generated during the state S2.

The input of the IMC 106 receives the RF signal via the RF cable 122from the output 116 and matches an impedance of the load coupled to theoutput of the IMC 106 with an impedance of the source coupled to theinput of the IMC 106 to generate a modified RF signal at the output ofthe IMC 106. The modified RF signal is sent via the RF transmission line124 to the lower electrode of the chuck 126. When the one or moreprocess gases are supplied between the upper electrode 128 and the chuck126 and the modified RF signal is supplied to the lower electrode 120,the one or more process gases are ignited to generate plasma within theplasma chamber 104. The plasma is used to process, e.g., etch, depositmaterials on, clean, sputter, etc., the substrate 130.

During each state S1 and S2, the sensor system 114 senses one or moreparameters, e.g., supplied voltage, reflected voltage, reflected power,supplied power, delivered power, complex impedance, voltage reflectioncoefficient, complex voltage and current, etc., at the output 116. Thesupplied power is RF power that is supplied by the RF signal that isgenerated by the RF generator 102. The reflected power is RF powerreflected towards the RF generator 102 as a result of impedance seen bythe RF generator 102 at the output 116 when the supplied power isprovided from the RF generator 102 to the IMC 106. For example, thereflected power includes power reflected from the plasma of the plasmachamber 108, via the RF transmission line 124, the IMC 106 and the RFcable 122 towards the RF generator 102. The voltage reflectioncoefficient is represented as a Greek symbol gamma (γ) and is a complexnumber that has a magnitude and a phase. The one or more parameters thatare sensed are sent from the sensor system 114 via the cable 136 to theprocessor 132. The processor 132 determines one or more variables fromthe one or more parameters. For example, the processor 132 identifiesthe one or more parameters that are measured and received from thesensor system 114, and stores the one or more parameters within thememory device 134. In this example, the one or more variables are theone or more parameters that are identified by the processor 132. Asanother example, the processor 132 calculates one or more factors, e.g.,gamma, frequency of the RF signal supplied via the output 116, etc.,from the one or more parameters, and stores the one or more factorswithin the memory device 134. In this example, the one or more variablesare the one or more factors that are calculated by the processor 132. Toillustrate, the processor 132 converts the RF signal supplied via theoutput 116 and having the supplied power from a time domain to afrequency domain to determine the frequency of the RF signal that issupplied via the output 116. As another illustration, gamma γ describeshow much of the supplied RF voltage of the RF signal generated andsupplied by the RF generator 102 is reflected towards the RF generator102. As yet another illustration, the gamma is calculated by theprocessor 132 a ratio of voltage of an RF signal that is reflectedtowards the RF generator 102 to voltage of the RF signal that isgenerated and supplied by the RF generator 102.

The processor 132 tunes, such as increases or decreases, increases in astep-wise fashion, or decreases in a step-wise fashion, the frequencyset point for the state S1 based on the one or more variables for thestate S1, such as measured during the state S1, and the one or morevariables for the state S2, such as measured during the state S2, togenerate a modified frequency set point for the state S1. During thestate S1, processor 132 sends the modified frequency set point for thestate S1 via the cable 138 to the DSP 110, which implements the modifiedfrequency set point for the state S1 in a manner described above. Forexample, during the state S1, the DSP 110 sends the modified frequencyset point for the state S1 to the auto-frequency tuner AFTS1, whichgenerates a command signal so that the RF signal that is generated bythe RF power supply 112 has the modified frequency set point. Toillustrate, upon receiving the modified frequency set point for thestate S1, the auto-frequency tuner AFTS1 determines an amount of currentsignal corresponding to, e.g., having a one-to-one relationship with,mapped to, linked to, etc., the modified frequency set point for thestate S1. Based on the amount of current that is to be generated by thedriver system 120 during the state S1, the auto-frequency tuner AFTS1generates a command signal and sends the command signal to the driversystem 120. During the state S1, in response to receiving the commandsignal, the driver system 120 generates and sends a current signalhaving the amount of current to the RF power supply 112. The RF powersupply 112, upon receiving the current signal generates the RF signalhaving the modified frequency set point for the state S1 and suppliesthe RF signal via the output 116 and the RF cable 122 to the input ofthe IMC 106.

Moreover, after the frequency set point for the state S1 is tuned, theprocessor 132 tunes, such as increases, decreases, or increases in astep-wise fashion, or decreases in a step-wise fashion, the frequencyset point for the state S2 based on the one or more variables measuredduring the state S1 and the one or more variables measured during thestate S2 to generate a modified frequency set point for the state S2.For example, the processor 132 does not tune the frequency set point forthe state S2 until the frequency set point for the state S1 is tuned.During the state S2, the processor 132 sends the modified frequency setpoint for the state S2 via the cable 138 to the DSP 110, whichimplements the modified frequency set point for the state S2 in a mannerdescribed above. For example, during the state S2, the DSP 110 sends themodified frequency set point for the state S2 to the auto-frequencytuner AFTS2, which generates a command signal so that the RF signal thatis generated by the RF power supply 112 has the modified frequency setpoint. To illustrate, upon receiving the modified frequency set pointfor the state S2, the auto-frequency tuner AFTS2 determines an amount ofcurrent signal corresponding to, e.g., having a one-to-one relationshipwith, mapped to, linked to, etc., the modified frequency set point forthe state S2. Based on the amount of current that is to be generated bythe driver system 120 during the state S2, the auto-frequency tunerAFTS2 generates a command signal and sends the command signal to thedriver system 120. During the state S2, in response to receiving thecommand signal, the driver system 120 generates and sends a currentsignal having the amount of current to the RF power supply 112. The RFpower supply 112, upon receiving the current signal generates the RFsignal having the modified frequency set point for the state S2 andsupplies the RF signal via the output 116 and the RF cable 122 to theinput of the IMC 106.

In some embodiments, the terms tuner and controller are usedinterchangeably herein. An example of an AFT is provided in U.S. Pat.No. 6,020,794, which is incorporated by reference herein in itsentirety.

In various embodiments, the power controllers PWRS1 and PWRS2, and theauto-frequency tuners AFTS1 and AFTS2 are modules, e.g., portions, etc.,of a computer program that is executed by the DSP 110.

In various embodiments, the power controllers PWRS1 and PWRS2, and theauto-frequency tuners AFTS1 and AFTS2 are separate integrated circuitsthat are coupled to an integrated circuit of the DSP 110. For example,the power controller PWRS1 is a first integrated circuit, the powercontroller PWRS2 is a second integrated circuit, the auto-frequencytuner AFTS1 is a third integrated circuit, the auto-frequency tunerAFTS2 is a fourth integrated circuit, and the DSP 110 is a fifthintegrated circuit. Each of the first through fourth integrated circuitis coupled to the fifth integrated circuit.

In some embodiments, an example of the state S1 of an RF signal includesthe power set point for the state S1 and the frequency set point for thestate S1. The power set point for the state S1 is an operational powerset point, which is a power level, such as an envelope or a zero-to-peakmagnitude, of the RF signal during the state S1. The frequency set pointfor the state S1 is an operational frequency set point, which is afrequency level, such as an envelope or a zero-to-peak magnitude, of theRF signal during the state S1. Similarly, an example of the state S2 ofthe RF signal includes the power set point for the state S2 and thefrequency set point for the state S2. The power set point for the stateS2 is an operational power set point, which is a power level, such as anenvelope or a zero-to-peak magnitude, of the RF signal during the stateS2. The frequency set point for the state S2 is an operational frequencyset point, which is a frequency level, such as an envelope or azero-to-peak magnitude, of the RF signal during the state S2.

In various embodiments, the power level for the state S2 is lower thanthe power level for the state S1. To illustrate, all power amounts of anRF signal from which the power level for the state S2 is generated arelower than all power amounts of the RF signal from which the power levelfor the state S1 is generated. In various embodiments, the power levelfor the state S2 is greater than the power level for the state S1. Toillustrate, all power amounts of the RF signal from which the powerlevel for the state S2 is generated are higher than all power amounts ofthe RF signal from which the power level for the state S1 is generated.In several embodiments, a level is generated from one or more amounts,e.g., values, magnitudes, etc. For example, a frequency level isgenerated from one or more frequency values of an RF signal and a powerlevel is generated from one or more power values of an RF signal. Tofurther illustrate, a frequency level is a root mean square value ofmultiple values of frequencies of an RF signal and a power level is aroot mean square value of multiple values of power of the RF signal.

In various embodiments, two or three RF generators are coupled to theIMC 106. For example, an additional RF generator is coupled to the IMC106 via an RF cable (not shown) to another input of the IMC 106. Theadditional RF generator is in addition to the RF generator 102. Theother input is not the same as the input to which the RF cable 122 iscoupled. The additional RF generator has the same structure and functionas that of the RF generator 102 except that the additional RF generatorhas a different operating frequency, e.g., 2 MHz, 27 MHz, 60 MHz, etc.,than that of the RF generator 102. For example, the RF generator 102 hasan operating frequency of 13.56 MHz and the additional RF generator hasan operating frequency of 2 MHz, or 400 kHz, or 27 MHz, or 60 MHz. TheIMC 106 combines the RF signals received from the RF generator 102 andthe additional RF generator, and matches an impedance of the loadcoupled to the output of the IMC 106 with that of the source, e.g., theRF generator 102, the additional RF generator, the RF cable 122, and theother RF cable, etc., to generate the modified RF signal at the outputof the IMC 106.

In one embodiment, the terms impedance matching circuit and impedancematching network are used herein interchangeably.

FIG. 2 is a flowchart of an embodiment of a method 200 for tuning thefrequency set points fs1 and fs2 based on the one or more variables forthe state S1 and the one or more variables for the state S2. The method200 is executed by the plasma tool 100 (FIG. 1). In an operation 202 ofthe method 200, a frequency set point fs1 for the state S1, a power setpoint Ps1 for the state S1, a frequency set point fs2 for the state S2,and a power set point Ps2 for the state S2 are set. For example, in amanner described above with reference to FIG. 1, the processor 132(FIG. 1) of the host computer 104 sends the set points fs1, Ps1, fs2,and Ps2 via the cable 138 (FIG. 1) to the DSP 110 (FIG. 1). The DSP 110sends the frequency set point fs1 to the auto-frequency tuner AFTS1, thefrequency set point fs2 to the auto-frequency tuner AFTS2, the power setpoint Ps1 to the power controller PWRS1, and the power set point Ps2 tothe power controller PWRS2. During the state S1, the power controllerPWRS1 and the auto-frequency tuner AFTS1 control the driver system 120and the RF power supply 112, in a manner described above, to generatethe RF signal having the power set point Ps1 and the frequency set pointfs1 at the output 116. Similarly, during the state S2, the powercontroller PWRS2 and the auto-frequency tuner AFTS2 control the driversystem 120 and the RF power supply 112, in a manner described above, togenerate the RF signal having the power set point Ps2 and the frequencyset point fs2 at the output 116.

Based on the one or more variables for the state S1 determined by theprocessor 132, in an operation 206 of the method 200, the processor 132determines to control a position of one or more of the electric circuitcomponents of the IMC 106. For example, the processor 132 determinesthat one of the variables, e.g., yS1, for the state S1 is not below apre-determined variable threshold for the state S1, e.g., pre-determinedgamma, etc., which is stored in the memory device 134. Upon determiningthat the one of the variables for the state S1 is not below thepre-determined variable threshold for the state S1, the processor 132sends a command signal via the cable 154 (FIG. 1) to the driver system150. Based on the command signal, the driver of the driver system 150generates a current signal and sends the current signal to the motor ofthe motor system 152 (FIG. 1). The motor rotates to rotate theconnection mechanism to further change a position of the circuitcomponent, e.g., a position of a plate of a capacitor, a position of acore of an inductor, etc., of the IMC 106 to modify an inductance and/ora capacitance of the IMC 106. In the operation 206, the processor 132continues to adjust one or more positions of the corresponding one ormore circuit components via the motor system 152 until the one of thevariables is below the pre-determined variable threshold.

In an operation 208 of the method 200, the processor 132 determineswhether the one of the variables for the state S1, e.g., γs1, is stable.For example, the processor 132 determines that all or a pre-determinednumber of values, such as magnitudes, of the one of the variables forthe state S1 lie within a pre-determined range for the state S1, e.g.,within a standard deviation of a pre-determined value of the one of thevariables for the state S1, etc. The pre-determined number of values ofthe one of the variables for the state S1 and the pre-determined rangeare stored in the memory device 134 for access by the processor 132. Theprocessor 132 determines that the one of the variables for the state S1is not stable upon determining that all or the pre-determined number ofvalues of the one of the variables for the state S1 lie outside thepre-determined range. On the other hand, the processor 132 determinesthat the one of the variables for the state S1 is stable upondetermining that all or the pre-determined number of values of the oneof the variables for the state S1 lie within the pre-determined range.

Upon determining that the one of the variables for the state S1 is notstable in the operation 208, an operation 209 of the method 200 isperformed. During the operation 209, a pre-determined step change, e.g.,a pre-determined step increase, a pre-determined step decrease, etc., ofa pre-determined step time is applied to the frequency set point fs1.For example, the processor 132 increases the frequency set point fs1 bya pre-determined step size ss1 to generate a frequency set point fs1+ss1for the pre-determined step time. The pre-determined step size and thepre-determined step time are stored in the memory device 134 for accessby the processor 132. In some embodiments, the pre-determined step sizeand the pre-determined step time are received from a user via aselection made using an input device, e.g., a keyboard, a mouse, akeypad, etc., that is coupled to the host computer 104. An example ofthe pre-determined step time is a portion, e.g., half, third,one-fourth, etc., of a time period for which the state S1 of the clockcycle of the pulsed signal 140 occurs. The frequency set point fs1+ss1is provided from the processor 132 to the DSP 110 via the cable 138. TheDSP 110 sends the frequency set point fs1+ss1 to the auto-frequencytuner AFTS1. During the state S1, the auto-frequency tuner AFTS1controls the driver system 120 and the RF power supply 112, in a mannerdescribed above, to generate an RF signal having the frequency set pointfs1+ss1 at the output 116. As another example, the processor 132decreases the frequency set point fs1 by the pre-determined step sizess1 to generate a frequency set point fs1−ss1 for the pre-determinedstep time. The frequency set point fs1−ss1 is provided from theprocessor 132 to the DSP 110 via the cable 138. The DSP 110 sends thefrequency set point fs1−ss1 to the auto-frequency tuner AFTS1. Duringthe state S1, the auto-frequency tuner AFTS1 controls the driver system120 and the RF power supply 112, in a manner described above, togenerate an RF signal having the frequency set point fs1−ss1 at theoutput 116. The operations 206, 208, and 209 are repeated until the oneof the variables for the state S1 is stable. In one embodiment, theoperations 208 and 209 are repeated without repeating the operation 206until the one of the variables for the state S1 is stable.

On the other hand, upon determining that the one of the variables forthe state S1 is stable in the operation 208, an operation 210 of themethod 200 is performed. In the operation 210, the processor 132determines that one of the variables for the state S2, such as γS2, isnot below a pre-set variable threshold for the state S2, e.g.,pre-determined gamma, etc., which is stored in the memory device 134.Upon determining that the one of the variables for the state S2 is notbelow the pre-set variable threshold for the state S2, a pre-set stepchange, e.g., a pre-set step increase, a pre-set step decrease, etc., ofa pre-set step time is applied to the frequency set point fs2. Forexample, upon determining that the one of the variables for the state S2is not below the pre-set variable threshold for the state S2, theprocessor 132 increases the frequency set point fs2 by thepre-determined step size ss2 to generate a frequency set point fs2+ss2for the pre-set step time. The pre-set step size and the pre-set steptime are stored in the memory device 134 for access by the processor132. In some embodiments, the pre-set step size and the pre-set steptime are received from the user via a selection made using the inputdevice that is coupled to the host computer 104. An example of thepre-set step time is a portion, e.g., half, third, one-fourth, etc., ofa time period for which the state S2 of the clock cycle of the pulsedsignal 140 occurs. The frequency set point fs2+ss2 is provided from theprocessor 132 to the DSP 110 via the cable 138. The DSP 110 sends thefrequency set point fs2+ss2 to the auto-frequency tuner AFTS2. Duringthe state S2, the auto-frequency tuner AFTS2 controls the driver system120 and the RF power supply 112, in a manner described above, togenerate an RF signal having the frequency set point fs2+ss2 at theoutput 116. In the operation 210, the processor 132 and the RF generator102 continue to adjust the frequency set point fs2+ss2 until the one ofthe variables is below the pre-set variable threshold for the state S2.As another example, upon determining that the one of the variables forthe state S2 is not below the pre-set variable threshold for the stateS2, the processor 132 decreases the frequency set point fs2 by thepre-determined step size ss2 to generate a frequency set point fs2−ss2for the pre-set step time. The frequency set point fs2−ss2 is providedfrom the processor 132 to the DSP 110 via the cable 138. The DSP 110sends the frequency set point fs2−ss2 to the auto-frequency tuner AFTS2.During the state S2, the auto-frequency tuner AFTS2 controls the driversystem 120 and the RF power supply 112, in a manner described above, togenerate an RF signal having the frequency set point fs2−ss2 at theoutput 116. In the operation 210, the processor 132 and the RF generator102 continue to adjust the frequency set point fs2−ss2 until the one ofthe variables is below the pre-set variable threshold for the state S2.The processor 132 continues to apply the pre-set step change in theoperation 210 until the one of the variables for the state S2 is belowthe pre-set variable threshold for the state S2.

In some embodiments, the pre-set variable threshold for the state S2 isthe same as the pre-determined variable threshold for the state S1. Invarious embodiments, the pre-set variable threshold for the state S2 isgreater than or less than the pre-determined variable threshold for thestate S1.

In an operation 212 of the method 200, the processor 132 determineswhether the one of the variables, e.g., γs2, for the state S2 is stable.For example, the processor 132 determines that all or a pre-set numberof values, such as magnitudes, of the one of the variables for the stateS2 lie within a pre-set range for the state S2, e.g., within a standarddeviation of a pre-set value of the one of the variables for the stateS2, etc. The pre-set number of values of the one of the variables forthe state S2 and the pre-set range are stored in the memory device 134for access by the processor 132. The processor 132 determines that theone of the variables for the state S2 is not stable upon determiningthat all or the pre-set number of values of the one of the variables forthe state S2 lie outside the pre-set range. On the other hand, theprocessor 132 determines that the one of the variables for the state S2is stable upon determining that all or the pre-set number of values ofthe one of the variables for the state S2 lie within the pre-set range.

In some embodiments, the pre-set number of values of the one of thevariables for the state S2 is the same as or different from, e.g.,greater than, less than, the pre-determined number of values of the oneof the variables for the state S1. In various embodiments, the pre-setrange for the state S2 is greater than or lower than the pre-determinedrange for the state S1.

Upon determining that the one of the variables for the state S2 is notstable in the operation 212, the operation 209 of the method 200 isperformed. During the operation 209, the pre-determined step increase ofthe pre-determined step time is applied to a frequency set point at thetime the operation 209 is performed. For example, when the frequency setpoint at the time before the operation 209 is performed is fs1, theprocessor 132 increases the frequency set point fs1 by thepre-determined step size ss1 to generate the frequency set point fs1+ss1for the pre-determined step time. The frequency set point fs1+ss1 isprovided from the processor 132 to the DSP 110 via the cable 138. TheDSP 110 sends the frequency set point fs1+ss1 to the auto-frequencytuner AFTS1. During the state S1, the auto-frequency tuner AFTS1controls the driver system 120 and the RF power supply 112, in a mannerdescribed above, to generate the RF signal having the frequency setpoint fs1+ss1 at the output 116. The operations 206, 208, 210, 212, and209 are repeated until the one of the variables for the state S2 isstable. As another example, when the frequency set point at the timebefore the operation 209 is performed is fs1, the processor 132decreases the frequency set point fs1 by the pre-determined step sizess1 to generate the frequency set point fs1−ss1 for the pre-determinedstep time. The frequency set point fs1−ss1 is provided from theprocessor 132 to the DSP 110 via the cable 138. The DSP 110 sends thefrequency set point fs1−ss1 to the auto-frequency tuner AFTS1. Duringthe state S1, the auto-frequency tuner AFTS1 controls the driver system120 and the RF power supply 112, in a manner described above, togenerate the RF signal having the frequency set point fs1−ss1 at theoutput 116. The operations 206, 208, 210, 212, and 209 are repeateduntil the one of the variables for the state S2 is stable.

As yet another example, when the frequency set point at the time beforethe operation 209 is performed is fs1+ss1, the processor 132 increasesthe frequency set point fs1+ss1 by the pre-determined step size ss1 togenerate a frequency set point fs1+ss1+ss1 for the pre-determined steptime. The frequency set point fs1+ss1+ss1 is provided from the processor132 to the DSP 110 via the cable 138. The DSP 110 sends the frequencyset point fs1+ss1+ss1 to the auto-frequency tuner AFTS1. During thestate S1, the auto-frequency tuner AFTS1 controls the driver system 120and the RF power supply 112, in a manner described above, to generatethe RF signal having the frequency set point fs1+ss1+ss1 at the output116. The operations 206, 208, 210, 212, and 209 are repeated until theone of the variables for the state S2 is stable. As still anotherexample, when the frequency set point at the time before the operation209 is performed is fs1−ss1, the processor 132 decreases the frequencyset point fs1−ss1 by the pre-determined step size ss1 to generate afrequency set point fs1−ss1−ss1 for the pre-determined step time. Thefrequency set point fs1−ss1−ss1 is provided from the processor 132 tothe DSP 110 via the cable 138. The DSP 110 sends the frequency set pointfs1−ss1−ss1 to the auto-frequency tuner AFTS1. During the state S1, theauto-frequency tuner AFTS1 controls the driver system 120 and the RFpower supply 112, in a manner described above, to generate the RF signalhaving the frequency set point fs1−ss1−ss1 at the output 116. Theoperations 206, 208, 210, 212, and 209 are repeated until the one of thevariables for the state S2 is stable.

In an operation 214 of the method 200, it is determined whether thepower set points Ps1 and Ps2 are met. For example, during the state S1,the sensor system 114 measures the supplied power of the RF signalgenerated and supplied by the RF generator 102, and provides themeasurement of supplied power via the cable 136 to the processor 132.The processor 132 determines whether the measurement of supplied powerfor the state S1 is within a pre-stored power limit from the power setpoint Ps1. The pre-stored power limit is stored within the memory device134. Upon determining that the measurement of supplied power for thestate S1 is not within the pre-stored power limit, the processor 132determines that the power set point Ps1 is not met and the operation 209is performed by the processor 132. For example, during the state S1,when the frequency set point at the time before the operation 209 isperformed is fs1, the processor 132 increases the frequency set pointfs1 by the pre-determined step size ss1 to generate the frequency setpoint fs1+ss1 for the pre-determined step time. The frequency set pointfs1+ss1 is provided from the processor 132 to the DSP 110 via the cable138. The DSP 110 sends the frequency set point fs1+ss1 to theauto-frequency tuner AFTS1. During the state S1, the auto-frequencytuner AFTS1 controls the driver system 120 and the RF power supply 112,in a manner described above, to generate the RF signal having thefrequency set point fs1+ss1 at the output 116. The operations 214, 209,206, 208, 210, 212, and 214 are repeated until the measurement ofsupplied power from the sensor system 114 is within the pre-stored powerlimit for the state S1. The pre-stored power limit is stored within thememory device 134. Upon determining that the measurement of suppliedpower for the state S1 is not within the pre-stored power limit, theoperation 209 is performed. As another example, when the frequency setpoint at the time before the operation 209 is performed is fs1, theprocessor 132 decreases the frequency set point fs1 by thepre-determined step size ss1 to generate the frequency set point fs1−ss1for the pre-determined step time. The frequency set point fs1−ss1 isprovided from the processor 132 to the DSP 110 via the cable 138. TheDSP 110 sends the frequency set point fs1−ss1 to the auto-frequencytuner AFTS1. During the state S1, the auto-frequency tuner AFTS1controls the driver system 120 and the RF power supply 112, in a mannerdescribed above, to generate the RF signal having the frequency setpoint fs1−ss1 at the output 116. The operations 209, 206, 208, 210, 212,and 214 are repeated until the measurement of supplied power from thesensor system 114 is within the pre-stored power limit for the state S1.

As yet another example, when the frequency set point at the time beforethe operation 209 is performed is fs1+ss1, the processor 132 increasesthe frequency set point fs1+ss1 by the pre-determined step size ss1 togenerate the frequency set point fs1+ss1+ss1 for the pre-determined steptime. The frequency set point fs1+ss1+ss1 is provided from the processor132 to the DSP 110 via the cable 138. The DSP 110 sends the frequencyset point fs1+ss1+ss1 to the auto-frequency tuner AFTS1. During thestate S1, the auto-frequency tuner AFTS1 controls the driver system 120and the RF power supply 112, in a manner described above, to generatethe RF signal having the frequency set point fs1+ss1+ss1 at the output116. The operations 209, 206, 208, 210, 212, and 214 are repeated untilthe measurement of supplied power from the sensor system 114 is withinthe pre-stored power limit for the state S1. As still another example,when the frequency set point at the time before the operation 209 isperformed is fs1−ss1, the processor 132 decreases the frequency setpoint fs1−ss1 by the pre-determined step size ss1 to generate thefrequency set point fs1−ss1−ss1 for the pre-determined step time. Thefrequency set point fs1−ss1−ss1 is provided from the processor 132 tothe DSP 110 via the cable 138. The DSP 110 sends the frequency set pointfs1−ss1−ss1 to the auto-frequency tuner AFTS1. During the state S1, theauto-frequency tuner AFTS1 controls the driver system 120 and the RFpower supply 112, in a manner described above, to generate the RF signalhaving the frequency set point fs1−ss1−ss1 at the output 116. Theoperations 209, 206, 208, 210, 212, and 214 are repeated until themeasurement of supplied power from the sensor system 114 is within thepre-stored power limit for the state S1.

As another example, during the state S2, the sensor system 114 measuresthe supplied power of the RF signal generated and supplied by the RFgenerator 102, and provides the measurement of supplied power via thecable 136 to the processor 132. The processor 132 determines whether themeasurement of supplied power for the state S2 is within a pre-set powerlimit of the power set point Ps2. The pre-set power limit is storedwithin the memory device 134. In some embodiments, the pre-set powerlimit for the state S2 is the same or different from the pre-storedpower limit for the state S1.

Upon determining that the measurement of supplied power for the state S2is not within the pre-set power limit for power for the state S2, theprocessor 132 determines that the power set point Ps2 is not met and theoperation 209 is performed by the processor 132. For example, when thefrequency set point at the time before the operation 209 is performed isfs1, during the state S1, the processor 132 increases the frequency setpoint fs1 by the pre-determined step size ss1 to generate the frequencyset point fs1+ss1 for the pre-determined step time. The frequency setpoint fs1+ss1 is provided from the processor 132 to the DSP 110 via thecable 138. The DSP 110 sends the frequency set point fs1+ss1 to theauto-frequency tuner AFTS1. During the state S1, the auto-frequencytuner AFTS1 controls the driver system 120 and the RF power supply 112,in a manner described above, to generate the RF signal having thefrequency set point fs1+ss1 at the output 116. The operations 209, 206,208, 210, 212, and 214 are repeated until the measurement of suppliedpower from the sensor system 114 is within the pre-set power limit forthe state S2. As another example, when the frequency set point at thetime before the operation 209 is performed is fs1, the processor 132decreases the frequency set point fs1 by the pre-determined step sizess1 to generate the frequency set point fs1−ss1 for the pre-determinedstep time. The frequency set point fs1−ss1 is provided from theprocessor 132 to the DSP 110 via the cable 138. The DSP 110 sends thefrequency set point fs1−ss1 to the auto-frequency tuner AFTS1. Duringthe state S1, the auto-frequency tuner AFTS1 controls the driver system120 and the RF power supply 112, in a manner described above, togenerate the RF signal having the frequency set point fs1−ss1 at theoutput 116. The operations 209, 206, 208, 210, 212, and 214 are repeateduntil the measurement of supplied power from the sensor system 114 iswithin the pre-set power limit for the state S2.

As another example, during the state S1, when the frequency set point atthe time before the operation 209 is performed is fs1+ss1, the processor132 increases the frequency set point fs1+ss1 by the pre-determined stepsize ss1 to generate the frequency set point fs1+ss1+ss1 for thepre-determined step time. The frequency set point fs1+ss1+ss1 isprovided from the processor 132 to the DSP 110 via the cable 138. TheDSP 110 sends the frequency set point fs1+ss1+ss1 to the auto-frequencytuner AFTS1. During the state S1, the auto-frequency tuner AFTS1controls the driver system 120 and the RF power supply 112, in a mannerdescribed above, to generate the RF signal having the frequency setpoint fs1+ss1+ss1 at the output 116. The operations 209, 206, 208, 210,212, and 214 are repeated until the measurement of supplied power fromthe sensor system 114 is within the pre-set power limit for the stateS2. As still another example, when the frequency set point at the timebefore the operation 209 is performed is fs1−ss1, the processor 132decreases the frequency set point fs1−ss1 by the pre-determined stepsize ss1 to generate the frequency set point fs1−ss1−ss1 for thepre-determined step time. The frequency set point fs1−ss1−ss1 isprovided from the processor 132 to the DSP 110 via the cable 138. TheDSP 110 sends the frequency set point fs1−ss1−ss1 to the auto-frequencytuner AFTS1. During the state S1, the auto-frequency tuner AFTS1controls the driver system 120 and the RF power supply 112, in a mannerdescribed above, to generate the RF signal having the frequency setpoint fs1−ss1−ss1 at the output 116. The operations 209, 206, 208, 210,212, and 214 are repeated until the measurement of supplied power fromthe sensor system 114 is within the pre-set power limit for the stateS2. The method 200 ends when the measurement of supplied power for thestate S1 is within the pre-stored power limit for the state S1 and themeasurement of supplied power for the state S2 is within the pre-setpower limit for the state S2.

FIG. 3 is a diagram of an embodiment of a graph 302 to illustrate thetwo states S1 and S2 of the RF signal that is generated by the RFgenerator 102 (FIG. 1) and a graph 304 to illustrate the two states S1and S2 of pulsed signal 140. The graph 302 plots supplied power at theoutput 116 versus time and the graph 304 also plots a logic level, suchas 0 or 1, of the pulsed signal 140. The RF signal that is generated bythe RF generator 102 alternates between the two states S1 and S2 byalternating between the two power set points Ps1 and Ps2. An example ofa power set point for a state is a root mean square (RMS) value of poweramounts for the state. Another example of a power set point for a stateis a zero-to-peak value of power amounts for the state. It should benoted that the power set point Ps2 is zero or an amount greater thanzero but less than the power set point Ps1. The pulsed signal 140alternates between the logic levels 1 and 0. The logic level 1 occursduring the state S1 of the pulsed signal 140 and the logic level 0occurs during the state S2 of the pulsed signal 140.

The power set points of the RF signal that is generated by the RFgenerator 102 are synchronized to the logic levels 1 and 0 of the pulsedsignal 140. For example, at a time of transition of from the logic level0 to the logic level 1, the RF signal that is generated by the RFgenerator 102 transitions from the power set point Ps2 to the power setpoint Ps1. As another example, at a time of transition of from the logiclevel 1 to the logic level 0, the RF signal that is generated by the RFgenerator 102 transitions from the power set point Ps1 to the power setpoint Ps2.

FIG. 4 is a diagram of embodiments of multiple Smith charts 402, 404,406, and 408 to illustrate that with an increase in power differencebetween the power set points Ps1 and Ps2, there is a decrease in atunable frequency range for the state S2. Each Smith chart plots animpedance or an admittance. For example, a resistance of the impedanceis plotted on an x-axis and a reactance of the impedance is plotted on ay-axis. A power difference between the power set points Ps1 and Ps2,e.g., between 1000 watts and 50 watts, etc., in the Smith chart 404 isgreater than a power difference between the power set points Ps1 andPs2, e.g., between 500 watts and 50 watts, etc., in the Smith chart 402.Similarly, a power difference, e.g., between 1500 watts and 50 watts,etc., between the power set points Ps1 and Ps2 in the Smith chart 406 isgreater than a power difference between the power set points Ps1 andPs2, e.g., between 1000 watts and 50 watts, etc., in the Smith chart404. Similarly, a power difference, e.g., between 2000 watts and 50watts, etc., between the power set points Ps1 and Ps2 in the Smith chart408 is greater than a power difference between the power set points Ps1and Ps2, e.g., between 1500 watts and 50 watts, etc., in the Smith chart406. With an increase in the power difference between the power setpoints Ps1 and Ps2, a range of the tunable frequency for the state S2 toachieve an impedance close to or of 50 ohms at the output 116 (FIG. 1)decreases as represented by plots 410, 412, 414, and 416.

The methods and systems described herein disclose that the one or morevariables determined in the states S1 and S2 are used to tune thefrequency in the state S1. By considering the one or more variables inboth the states S1 and S2, the frequency in the state S1 is tuned toachieve an impedance close to or of 50 ohms at the output 116 (FIG. 1)to further reduce power that is reflected towards the RF generator 102.

FIG. 5 is a diagram of embodiments of multiple Smith charts 502, 504,and 506 to illustrate that a change in the frequency set point for thestate S1 helps achieve a desirable plasma impedance at the output 116.The Smith chart 502 plots an impedance 508, the Smith chart 504 plots animpedance 510, and the Smith chart 506 plots an impedance 512. Thedesirable plasma impedance is achieved at a point 514 on the Smithcharts 502, 504, and 506. Again, by considering the one or morevariables for the states S1 and S2 in tuning the frequency for the stateS1, the desirable plasma impedance at the point 514 is achieved.

FIG. 6A is a diagram of an embodiment of a method 600 for tuning thefrequency set points fs1 and fs2 based on the one or more variables forthe state S1 and the one or more variables for the state S2.

FIG. 6B is a diagram of an embodiment of a method 650 for tuning thefrequency set points fs1 and fs2 based on the one or more variables forthe state S1 and the one or more variables for the state S2.

It should be noted that the embodiments described herein are describedusing two states. In some embodiments, three or more than three statesmay be used.

Embodiments described herein may be practiced with various computersystem configurations including hand-held hardware units, microprocessorsystems, microprocessor-based or programmable consumer electronics,minicomputers, mainframe computers and the like. The embodiments canalso be practiced in distributed computing environments where tasks areperformed by remote processing hardware units that are linked through anetwork.

In some embodiments, a controller is part of a system, which may be partof the above-described examples. Such systems include semiconductorprocessing equipment, including a processing tool or tools, chamber orchambers, a platform or platforms for processing, and/or specificprocessing components (a wafer pedestal, a gas flow system, etc.). Thesesystems are integrated with electronics for controlling their operationbefore, during, and after processing of a semiconductor wafer orsubstrate. The electronics is referred to as the “controller,” which maycontrol various components or subparts of the system or systems. Thecontroller, depending on the processing requirements and/or the type ofsystem, is programmed to control any of the processes disclosed herein,including the delivery of process gases, temperature settings (e.g.,heating and/or cooling), pressure settings, vacuum settings, powersettings, RF generator settings, RF matching circuit settings, frequencysettings, flow rate settings, fluid delivery settings, positional andoperation settings, wafer transfers into and out of a tool and othertransfer tools and/or load locks coupled to or interfaced with a system.

Broadly speaking, in a variety of embodiments, the controller is definedas electronics having various integrated circuits, logic, memory, and/orsoftware that receive instructions, issue instructions, controloperation, enable cleaning operations, enable endpoint measurements, andthe like. The integrated circuits include chips in the form of firmwarethat store program instructions, digital signal processors (DSPs), chipsdefined as ASICs, PLDs, and/or one or more microprocessors, ormicrocontrollers that execute program instructions (e.g., software). Theprogram instructions are instructions communicated to the controller inthe form of various individual settings (or program files), defining theparameters, the factors, the variables, etc., for carrying out aparticular process on or for a semiconductor wafer or to a system. Theprogram instructions are, in some embodiments, a part of a recipedefined by process engineers to accomplish one or more processing stepsduring the fabrication of one or more layers, materials, metals, oxides,silicon, silicon dioxide, surfaces, circuits, and/or dies of a wafer.

The controller, in some embodiments, is a part of or coupled to acomputer that is integrated with, coupled to the system, otherwisenetworked to the system, or a combination thereof. For example, thecontroller is in a “cloud” or all or a part of a fab host computersystem, which allows for remote access of the wafer processing. Thecomputer enables remote access to the system to monitor current progressof fabrication operations, examines a history of past fabricationoperations, examines trends or performance metrics from a plurality offabrication operations, to change parameters of current processing, toset processing steps to follow a current processing, or to start a newprocess.

In some embodiments, a remote computer (e.g. a server) provides processrecipes to a system over a network, which includes a local network orthe Internet. The remote computer includes a user interface that enablesentry or programming of parameters and/or settings, which are thencommunicated to the system from the remote computer. In some examples,the controller receives instructions in the form of data, which specifythe parameters, factors, and/or variables for each of the processingsteps to be performed during one or more operations. It should beunderstood that the parameters, factors, and/or variables are specificto the type of process to be performed and the type of tool that thecontroller is configured to interface with or control. Thus as describedabove, the controller is distributed, such as by including one or morediscrete controllers that are networked together and working towards acommon purpose, such as the processes and controls described herein. Anexample of a distributed controller for such purposes includes one ormore integrated circuits on a chamber in communication with one or moreintegrated circuits located remotely (such as at the platform level oras part of a remote computer) that combine to control a process on thechamber.

Without limitation, in various embodiments, example systems to which themethods are applied include a plasma etch chamber or module, adeposition chamber or module, a spin-rinse chamber or module, a metalplating chamber or module, a clean chamber or module, a bevel edge etchchamber or module, a physical vapor deposition (PVD) chamber or module,a chemical vapor deposition (CVD) chamber or module, an atomic layerdeposition (ALD) chamber or module, an atomic layer etch (ALE) chamberor module, an ion implantation chamber or module, a track chamber ormodule, and any other semiconductor processing systems that isassociated or used in the fabrication and/or manufacturing ofsemiconductor wafers.

It is further noted that in some embodiments, the above-describedoperations apply to several types of plasma chambers, e.g., a plasmachamber including an inductively coupled plasma (ICP) reactor, atransformer coupled plasma chamber, conductor tools, dielectric tools, aplasma chamber including an electron cyclotron resonance (ECR) reactor,etc. For example, one or more RF generators are coupled to an inductorwithin the ICP reactor. Examples of a shape of the inductor include asolenoid, a dome-shaped coil, a flat-shaped coil, etc.

As noted above, depending on the process step or steps to be performedby the tool, the host computer communicates with one or more of othertool circuits or modules, other tool components, cluster tools, othertool interfaces, adjacent tools, neighboring tools, tools locatedthroughout a factory, a main computer, another controller, or tools usedin material transport that bring containers of wafers to and from toollocations and/or load ports in a semiconductor manufacturing factory.

With the above embodiments in mind, it should be understood that some ofthe embodiments employ various computer-implemented operations involvingdata stored in computer systems. These operations are those physicallymanipulating physical quantities. Any of the operations described hereinthat form part of the embodiments are useful machine operations.

Some of the embodiments also relate to a hardware unit or an apparatusfor performing these operations. The apparatus is specially constructedfor a special purpose computer. When defined as a special purposecomputer, the computer performs other processing, program execution orroutines that are not part of the special purpose, while still beingcapable of operating for the special purpose.

In some embodiments, the operations may be processed by a computerselectively activated or configured by one or more computer programsstored in a computer memory, cache, or obtained over the computernetwork. When data is obtained over the computer network, the data maybe processed by other computers on the computer network, e.g., a cloudof computing resources.

One or more embodiments can also be fabricated as computer-readable codeon a non-transitory computer-readable medium. The non-transitorycomputer-readable medium is any data storage hardware unit, e.g., amemory device, etc., that stores data, which is thereafter be read by acomputer system. Examples of the non-transitory computer-readable mediuminclude hard drives, network attached storage (NAS), ROM, RAM, compactdisc-ROMs (CD-ROMs), CD-recordables (CD-Rs), CD-rewritables (CD-RWs),magnetic tapes and other optical and non-optical data storage hardwareunits. In some embodiments, the non-transitory computer-readable mediumincludes a computer-readable tangible medium distributed over anetwork-coupled computer system so that the computer-readable code isstored and executed in a distributed fashion.

Although the method operations above were described in a specific order,it should be understood that in various embodiments, other housekeepingoperations are performed in between operations, or the method operationsare adjusted so that they occur at slightly different times, or aredistributed in a system which allows the occurrence of the methodoperations at various intervals, or are performed in a different orderthan that described above.

It should further be noted that in an embodiment, one or more featuresfrom any embodiment described above are combined with one or morefeatures of any other embodiment without departing from a scopedescribed in various embodiments described in the present disclosure.

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, it will be apparent thatcertain changes and modifications can be practiced within the scope ofappended claims. Accordingly, the present embodiments are to beconsidered as illustrative and not restrictive, and the embodiments arenot to be limited to the details given herein.

The invention claimed is:
 1. A method for achieving reduction in powerreflected towards a radio frequency (RF) generator, comprising:providing a plurality of set points to the RF generator, wherein the setpoints include a frequency set point for a first state of a digitalpulsed signal, a frequency set point for a second state of the digitalpulsed signal, a power set point for the first state of the digitalpulsed signal, and a power set point for the second state of the digitalpulsed signal; adjusting an impedance matching circuit to reduce avariable for the first state to be below a pre-determined variablethreshold, wherein the variable is associated with the RF generator;determining whether the variable for the first state is stable;adjusting the frequency set point for the second state upon determiningthat the variable for the first state is stable, wherein said adjustingthe frequency set point for the second state is performed to reduce avariable for the second state to be lower than a pre-set variablethreshold; determining whether the variable for the second state isstable; and changing the frequency set point for the first state inresponse to determining that the variable for the second state is notstable to achieve the reduction in power reflected towards the RFgenerator.
 2. The method of claim 1, further comprising changing thefrequency set point for the first state in response to determining thatthe variable for the first state is not stable.
 3. The method of claim1, further comprising: determining whether the power set point for thefirst state is achieved; and changing the frequency set point for thefirst state upon determining that the power set point for the firststate is not achieved.
 4. The method of claim 1, further comprising:determining whether the power set point for the second state isachieved; and changing the frequency set point for the first state upondetermining that the power set point for the second state is notachieved.
 5. The method of claim 1, wherein the variable associated withthe RF generator is measured at an output of the RF generator.
 6. Themethod of claim 1, wherein the variable for the first state includes amagnitude of a voltage reflection coefficient, wherein said determiningwhether the variable for the first state is stable includes determiningwhether the magnitude of the voltage reflection coefficient measuredduring the first state is stable.
 7. The method of claim 1, wherein thevariable for the second state includes a magnitude of a voltagereflection coefficient, wherein said determining whether the variablefor the second state is stable includes determining whether themagnitude of the voltage reflection coefficient measured during thesecond state is stable.
 8. The method of claim 1, wherein the frequencyset point for the first state is a value of frequency of an RF signal tobe supplied by the RF generator during the first state, wherein thefrequency set point for the second state is a value of frequency of theRF signal to be supplied by the RF generator during the second state,wherein the power set point for the first state is a value of power ofthe RF signal to be supplied by the RF generator during the first state,wherein the power set point for the second state is a value of power ofthe RF signal to be supplied by the RF generator during the secondstate.
 9. A system for achieving reduction in power reflected towards aradio frequency (RF) generator, comprising: an RF generator configuredto generate an RF signal; an impedance matching network coupled to theRF generator for receiving the RF signal to generate a modified RFsignal; a plasma chamber coupled to the impedance matching network forreceiving the modified RF signal; a host computer system coupled to theRF generator, wherein the host computer system includes a processorconfigured to: provide a plurality of set points to the RF generator,wherein the set points include a frequency set point for a first stateof a digital pulsed signal, a frequency set point for a second state ofthe digital pulsed signal, a power set point for the first state of thedigital pulsed signal, and a power set point for the second state of thedigital pulsed signal; adjust the impedance matching network to reduce avariable for the first state to be below a pre-determined variablethreshold, wherein the variable for the first state is associated withthe RF generator; determine whether the variable for the first state isstable; adjust the frequency set point for the second state upondetermining that the variable for the first state is stable, wherein thefrequency set point for the second state is adjusted to reduce avariable for the second state to be lower than a pre-set variablethreshold; determine whether the variable for the second state isstable; and change the frequency set point for the first state inresponse to determining that the variable for the second state is notstable to achieve the reduction in power reflected towards the RFgenerator.
 10. The system of claim 9, wherein the processor is furtherconfigured to change the frequency set point for the first state inresponse to determining that the variable for the first state is notstable.
 11. The system of claim 9, wherein the processor is furtherconfigured to: determine whether the power set point for the first stateis achieved; and change the frequency set point for the first state upondetermining that the power set point for the first state is notachieved.
 12. The system of claim 9, wherein the processor is furtherconfigured to: determine whether the power set point for the secondstate is achieved; and change the frequency set point for the firststate upon determining that the power set point for the second state isnot achieved.
 13. The system of claim 9, wherein the variable associatedwith the RF generator is measured at an output of the RF generator. 14.The system of claim 9, wherein the variable for the first state includesa magnitude of a voltage reflection coefficient, wherein to determinewhether the variable for the first state is stable, the processor isconfigured to determine whether the magnitude of the voltage reflectioncoefficient measured during the first state is stable.
 15. The system ofclaim 9, wherein the variable for the second state includes a magnitudeof a voltage reflection coefficient, wherein to determine whether thevariable for the second state is stable, the processor is configured todetermine whether the magnitude of the voltage reflection coefficientmeasured during the second state is stable.
 16. The system of claim 9,wherein the frequency set point for the first state is a value offrequency of the RF signal to be supplied by the RF generator during thefirst state, wherein the frequency set point for the second state is avalue of frequency of the RF signal to be supplied by the RF generatorduring the second state, wherein the power set point for the first stateis a value of power of the RF signal to be supplied by the RF generatorduring the first state, wherein the power set point for the second stateis a value of power of the RF signal to be supplied by the RF generatorduring the second state.
 17. A non-transitory computer readable mediumstoring a program causing a computer to execute a plurality ofoperations for achieving a reduction in power reflected towards a radiofrequency (RF) generator, the operations comprising: providing aplurality of set points to the RF generator, wherein the set pointsinclude a frequency set point for a first state of a digital pulsedsignal, a frequency set point for a second state of the digital pulsedsignal, a power set point for the first state of the digital pulsedsignal, and a power set point for the second state of the digital pulsedsignal; adjusting an impedance matching circuit to reduce a variable forthe first state to be below a pre-determined variable threshold, whereinthe variable is associated with the RF generator; determining whetherthe variable for the first state is stable; adjusting the frequency setpoint for the second state upon determining that the variable for thefirst state is stable, wherein said adjusting the frequency set pointfor the second state is performed to reduce a variable for the secondstate to be lower than a pre-set variable threshold; determining whetherthe variable for the second state is stable; and changing the frequencyset point for the first state in response to determining that thevariable for the second state is not stable to achieve the reduction inpower reflected towards the RF generator.
 18. The non-transitorycomputer readable medium of claim 17, wherein the operations furthercomprise changing the frequency set point for the first state inresponse to determining that the variable for the first state is notstable.
 19. The non-transitory computer readable medium of claim 17,wherein the operations further comprise: determining whether the powerset point for the first state is achieved; and changing the frequencyset point for the first state upon determining that the power set pointfor the first state is not achieved.
 20. The non-transitory computerreadable medium of claim 17, wherein the operations further comprise:determining whether the power set point for the second state isachieved; and changing the frequency set point for the first state upondetermining that the power set point for the second state is notachieved.
 21. The non-transitory computer readable medium of claim 17,wherein the variable associated with the RF generator is measured at anoutput of the RF generator.
 22. The non-transitory computer readablemedium of claim 17, wherein the variable for the first state includes amagnitude of a voltage reflection coefficient, wherein the operation ofdetermining whether the variable for the first state is stable includesdetermining whether the magnitude of the voltage reflection coefficientmeasured during the first state is stable.
 23. The non-transitorycomputer readable medium of claim 17, wherein the variable for thesecond state includes a magnitude of a voltage reflection coefficient,wherein the operation of determining whether the variable for the secondstate is stable includes determining whether the magnitude of thevoltage reflection coefficient measured during the second state isstable.
 24. The non-transitory computer readable medium of claim 17,wherein the frequency set point for the first state is a value offrequency of an RF signal to be supplied by the RF generator during thefirst state, wherein the frequency set point for the second state is avalue of frequency of the RF signal to be supplied by the RF generatorduring the second state, wherein the power set point for the first stateis a value of power of the RF signal to be supplied by the RF generatorduring the first state, wherein the power set point for the second stateis a value of power of the RF signal to be supplied by the RF generatorduring the second state.